Effects of acetylcholine on resting and action potentials, and on contractile force in the ventricle of Dolabella auricularia.

Acetylcholine (2 x io" to 2 x io~ M) depolarized the isolated ventricle of Dolabella auricularia. The depolarization was accompanied by a negatively inotropic effect from 2 x io~* M to 2 x io~* M, and by a positively tonotropic effect from 2 x io~* M to 2 x icr M. The interaction of acetylcholine and 5-hydroxytryptamine was studied by artificially prolonging the plateau of the cardiac action potential by treatment with 5-HT. Acetylcholine had the effect of shortening the plateau established by 5-hydroxytryptamine. Force was reduced correspondingly.